Revealing mistake: When the weasels are in Valiant's apartment and the leader says, "Step outta line and we'll hang you and your laundry out to dry," you can see the shadow of the mechanical arm used to hold the gun cast on Hoskins. (00:42:50)
Continuity mistake: In the scene where Valiant is sitting in the Night Club and meets Betty they start to talk. Notice she puts down her tray off to the side, in the next shot the tray is nowhere to be seen. (00:17:40)
Visible crew/equipment: In the scene where the weasels are chasing Roger and Hoskins and the weasel says, " I'm going to blow his head off ", look at their icon on the side of their door then quickly look to the left you can see the bumper and back end of the car that is driving the camera. (00:56:05)
Factual error: Look carefully at the electric trolleys trundling around the streets (and that Valiant hitches a ride on). You'll see that although they have boom arms on top, which are usually hoisted up and connected to overhead powerlines, there are no overhead wires anywhere for them to be getting electricity from. [Notice in the scene when Valiant gives Dolores the check, a Red Car Trolly passes outside the window and sparks fly from the overhead wire contacts. In all of the scenes outside the bar the wires are gone]. (00:10:10)
Factual error: The Goofy cartoon Roger watches in the theater was made in 1949, but the film takes place in 1947. (00:59:50)
Continuity mistake: At Maroon's office in the beginning Eddie is holding a newspaper. The way he holds it changes between the shots. (00:06:10)
Revealing mistake: When Wheezy and Psycho laugh at Smart Guy after he has fallen down the stairs, if you look closely you can see the wires holding Wheezy's machine gun up. (00:42:20)
Continuity mistake: When Eddie Valiant gets thrown in the garbage by the gorilla he stands up and there is some trash on his back and hat, but when the camera changes shot the trash is gone. (00:21:25)
Revealing mistake: When Judge Doom knocks Eddie off the Dip machine, note the Acme Curve Ball boxes in the background that appear to be written backwards, revealing a flipped shot. (01:26:30)
Revealing mistake: When Daffy gets thrown into Donald's grand piano, a wire is visible on the upper left side of the screen - closing the lid on his beak. (00:15:40)
Visible crew/equipment: A crew member's hand is visible turning the steering wheel of Eddie's beat-up Plymouth when Roger skids it to a halt. (01:17:35)
Revealing mistake: During the piano duel finale, Donald blasts a cannon at Daffy and the grand piano collapses - seemingly from the impact. But if you look closely there are actually ropes pulling the piano's legs from somewhere offstage. (00:17:05)
Visible crew/equipment: Set lights are visible on the ceiling for a few shots in the scene where Eddie and Baby Herman are discussing Marvin Acme's will. (00:34:30)
Revealing mistake: When Eddie and Roger are using Benny the Cab to run from the weasels, Eddie reverses gears and backs into the alley. It may be Benny the Cab's image onscreen, but a shadow on the ground actually reveals the go-cart which Eddie uses for the take. (00:58:40)
Visible crew/equipment: When Eddie grabs a newspaper from Baby Herman, you can briefly see the mechanical arm used to hold it - sticking out of the carriage for a split second. (00:35:00)
Revealing mistake: After Lena Hyena plants a kiss on Eddie, he tumbles down the street and lands face-first onto a solid white line. Pavement is animated into this shot, however a reflection of the stage floor is still visible. (01:13:20)
Revealing mistake: As Roger gets ready to take a drink of bourbon in R.K. Maroon's office you can see a moving shadow on the desktop - which is that of a mechanical arm used to hold the shot glass. (00:23:40)
Revealing mistake: After Eddie tells Roger that his handcuff keys are missing, they leap over the bed as the Toon Patrol sirens approach. When Eddie lands on the floor, his bedsheets get disturbed by a large blast of air - most likely the backfire of a safety cushion that was hidden behind the desk to break his fall. (00:40:10)
Visible crew/equipment: In one shot where Eddie leaps into a wall of pogo stick boxes at the Acme factory, a springboard used for the stunt is partially visible behind the red banana skin containers. (01:24:35)
Revealing mistake: At one point where Roger drags Eddie over to the electrical outlet spy hole in Dolores' secret room, Roger says "This will be a great place to hide." Both of them are handcuffed together in this shot, but Roger's shadow is not animated into his cuff. (00:44:20)
Answer: Valiant also shares his name with Arthurian comic strip hero Prince Valiant, who wields a singing sword, Flamberge.